Patent Literature 1, for example, describes a conventional fuel supply device which includes a fuel tank, a fuel pump unit installed inside the fuel tank, and a controller for the fuel pump unit. The fuel supply device includes a chamber that accommodates the controller, and a lid member that covers the opening of the chamber. The lid member has a higher fuel permeability than the chamber.
In the fuel supply device disclosed in Patent Literature 1, as described above, the lid member has a higher fuel permeability than the chamber. Therefore, when fuel vapor flows into the chamber, the fuel vapor can be discharged to the external atmosphere through the lid member. However, since the fuel vapor is heavier than the air, the fuel vapor accumulates from the bottom of the chamber. Therefore, the fuel vapor contacts the lid part only after the chamber has been filled with the fuel vapor. During this time, the controller stored in the chamber is kept in contact with the fuel vapor, and therefore may be damaged.